The present invention relates to auto theft prevention systems and more particularly to an electronic lock system for an auto ignition which prevents "hot wiring" and other unauthorized over riding of an auto ignition.
Contemporary ignition locks provide virtually no detriment to theft, since the lock can be jumpered or, alternatively, the ignition and starter circuits can be controlled directly from within the engine compartment. To preclude this, the engine compartment must be made secure and unauthorized access to the lock code denied.
To accomplish this according to the present invention, the engine compartment may be secured by an electromechanical disconnect in the hood latching mechanism, such that when unenergized the latch-release handle disconnects from the latching mechanism. Such a device may not have much mechanical strength nor require but little electrical power to operate. Further, the lock code is secured as by locating it in the secured engine compartment. The key code may then be transduced, in the open, to an electrical format, and transmitted to the secured compartment for comparison with the lock code. A match of the codes may then permit both normal engine operation and access to the secured compartment.
It is a practical necessity that the legimate user not be penalized by the security system. In the present invention this is simply accomplished by adding an electronic code to the standard ignition key and by modifying the standard ignition lock to also serve as a code transducer. No additional action or time delay is imposed on the legitimate user.
Unfortunately, since such an electronic lock system is inherently capable of very high speed operation, it is vulnerable to unauthorized operation in response to high-speed electronic code generators unless appropriate countermeasures are taken. In the present invention, the system includes time delay means to prevent operation by a code generator. For example, in one form of the invention a first coded word from a code generator may be accepted without penalty. If it is the correct code, there is no further input needed or given while the system is energized. However, if it is incorrect, a subsequent code sequence will preclude acceptance of all further data while the ignition system is energized. To escape from such a lock out mode, the system must be de-energized and then re-energized. After a time delay, such as one second, from de-energization, the system will again accept one code sequence. Thus, an electronic code generator can not effectively generate trial sequences faster than one per second. In addition to the time delay, there must be a sufficient number of possible codes to make the trial of all possible sequences adequately long. For a 16-bit lock code, for example, at one sequence per second, requires 18 hours for all sequences.
In addition, the electronic lock must be protected from brute-force entry. For example, over-voltage or reverse polarity may cause circuitry to fail in a manner permitting access. In the present invention, such entry is precluded by shunting Zener diodes across each access line, such that there is zener conduction if the applied voltage is much above normal and forward diode conduction if reverse polarity is applied. Further, each such line is fused so that either event will open the circuit.
The foregoing and other features of the present invention may be more clearly understood by reference to the following detailed description, when considered with the drawings which by way of example illustrate one form of electronic lock system embodying the features of the present invention.